One known type of monitoring system for the detection of a gas leakage is disclosed in U.S. Pat. No. 3,955,186. The electric circuitry used in this safety system applies a combination of solid state devices, mechanical relays and switches. Such relays and switches are expensive, heavy in weight, take up much space and require extensive wiring. Moreover, as they enter into operation only rarely they are sources of faults and malfunctions. The system makes use of a multivibrator to supply the heater of the gas sensor rated at 0.5 volt with short duration current pulses with a mark space ratio of 50:1. This means a peak power of approximately 24 W which constitutes a considerable loss for the power supply.
Gas monitoring systems designed to provide protection against fires and explosions caused by uncontrolled gas leakage in kitchens and other places using gas as a source of energy must employ a magnetic valve to shut-off gas flow by means of a gas sensor. To obtain full security and protection at all times, the valve must be closed under normal conditions and energized to the open position by a very small current. If the system does not operate due to an electrical or a system failure, the valve remains closed, stopping gas flow from its source and creating a big problem for the user as he is left without gas and energy until the power is restored or until a qualified technician repairs the system. This problem is especially severe in areas where gas is often the only source of energy and where repair due to remoteness of places can take several days.